阅读说明：本技术 基于afm的页岩孔隙度计算及组分孔隙贡献评价方法 (Shale porosity calculation and component porosity contribution evaluation method based on AFM ) 是由 陈尚斌 李学元 陈司 龚卓 王阳 王慧军 于 2020-06-30 设计创作，主要内容包括：本发明公开基于AFM的页岩孔隙度计算及组分孔隙贡献评价方法,包括如下步骤：S1、通过处理后的AFM数据提取出页岩表面三维高程数据和相位数据,对页岩表面三维高程数据进行校正；S2、采用阈值法,选取高度阈值,分割出孔隙函数,求取孔体积,根据孔隙度定义,计算出页岩孔隙度；S3、采用双阈值离散积分法,得到相位孔隙函数,利用相位孔隙函数计算不同相位区间内的孔隙度,将不同相位区间内的孔隙度和页岩物质成分进行线性拟合并计算它们之间的相关系数,以此来评价不同组分的孔隙贡献。本发明提供的基于AFM的页岩孔隙度计算及组分孔隙贡献评价方法,拓宽了AFM在非常规油气领域的应用范围。(The invention discloses a shale porosity calculation and component pore contribution evaluation method based on AFM, which comprises the following steps: s1, extracting shale surface three-dimensional elevation data and phase data through the processed AFM data, and correcting the shale surface three-dimensional elevation data; s2, selecting a height threshold value by adopting a threshold value method, segmenting a pore function, calculating pore volume, and calculating the porosity of the shale according to the definition of the porosity; s3, obtaining a phase pore function by adopting a dual-threshold discrete integration method, calculating the porosity in different phase intervals by utilizing the phase pore function, performing linear fitting on the porosity and the shale material composition in the different phase intervals, and calculating a correlation coefficient between the porosity and the shale material composition so as to evaluate the pore contributions of different components. The method for calculating the porosity of the shale and evaluating the contribution of the component pores based on the AFM widens the application range of the AFM in the field of unconventional oil and gas.)

1. The shale porosity calculation and component porosity contribution evaluation method based on AFM is characterized by comprising the following steps:

s1, extracting shale surface three-dimensional elevation data and phase data through the processed AFM data, and correcting the shale surface three-dimensional elevation data;

s2, selecting a height threshold value by adopting a threshold value method, segmenting a pore function, calculating pore volume, and calculating the porosity of the shale according to the definition of the porosity;

s3, obtaining a phase pore function by adopting a dual-threshold discrete integration method, calculating the porosity in different phase intervals by utilizing the phase pore function, performing linear fitting on the porosity and the shale material composition in the different phase intervals, and calculating a correlation coefficient between the porosity and the shale material composition so as to evaluate the pore contributions of different components.

2. The method for calculating shale porosity and evaluating contribution of component pores based on AFM of claim 1, wherein in step S1, the elevation correction is performed on the three-dimensional coordinate data of shale surface topography with the elevation of the lowest point of the shale surface as a zero-datum elevation.

3. The method for calculating the porosity of the shale and evaluating the contribution of the porosity of the shale based on the AFM as claimed in claim 1, wherein in the step S2, the specific step of obtaining the pore volume is as follows:

selecting a proper height threshold value, segmenting a pore function, regarding the projection of the surface of the sample on an xOy coordinate system as a virtual plane with negligible thickness, and cutting the surface of the sample from bottom to top by using the virtual plane, wherein the volume enclosed by the virtual plane and the surface of the sample lower than the plane is the pore volume, and the calculation formula is as follows:

wherein g (x, y) is a pore function; f (x, y) is an elevation function; t is a height threshold, m; v is the pore volume, m³(ii) a A is the projected area, m²(ii) a h is elevation, m; a and b are the projected width and length, m, respectively.

4. The AFM-based shale porosity calculation and component porosity contribution evaluation method according to claim 1, wherein the step of calculating the shale porosity in the step S2 is as follows:

the volume is divided by the product of the projected area and the selected elevation, and is calculated as:

wherein phi is porosity,%.

5. The method for calculating the porosity of shale and evaluating the contribution of the porosity of shale based on AFM of claim 1, wherein the dual-threshold discrete integration method in the step S3 specifically comprises:

on the basis of calculating the porosity by performing a threshold method on the elevation data once, performing a threshold method on the phase data once again, selecting a phase threshold value P, and segmenting a phase pore function, wherein the calculation formula is as follows:

where ξ (x, y) is the phase pore function; p is the phase threshold.

6. The method according to claim 1, wherein in the step S3, the porosity in different phase intervals is calculated by using a phase porosity function, specifically:

integrating the difference between the elevation and the phase aperture function, and dividing the result by the product of the plane projection area and the elevation threshold value, wherein the formula is as follows:

wherein phi is_ξIs the phase porosity,%.

Technical Field

The invention relates to a shale porosity calculation and component pore contribution evaluation method based on an AFM (atomic force microscopy), and belongs to the field of shale gas geology.

Background

Shale gas plays an increasingly important role in the world energy field. Shale gas reservoirs usually develop multi-scale micro-nano pore cracks, the pore structures are complex, the microscopic heterogeneity is obvious, and the success rate of exploration and development is limited. The material composition of shale is the basis for the development of the pore system, however the contribution of the different components of the reservoir to the pores is not clear. The method has important significance for understanding the pore structure of the shale gas reservoir, distinguishing the pore contribution of main material components, accurately evaluating shale gas resources, revealing shale gas reservoir formation mechanism and guiding favorable area division.

The Atomic Force Microscope (AFM) technology can be used for qualitative and quantitative characterization of a shale pore structure, but the atomic force microscope cannot directly measure the shale porosity, and the porosity is an extremely important parameter for unconventional reservoir evaluation, so that the extensive application of the AFM in the unconventional oil and gas field is limited to a certain extent. Research has shown that the change of AFM phase is closely related to material composition, which provides a theoretical basis for evaluating the pore contribution of the main material composition by AFM, but no related research has been made.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides the shale porosity calculation and component porosity contribution evaluation method based on the AFM, which makes up the defects of the AFM in the aspect of measuring the shale porosity and promotes the combination of the mineral analysis capability and the pore structure measurement capability of the AFM.

In order to achieve the purpose, the method for calculating the porosity of the shale and evaluating the contribution of the component pores based on the AFM comprises the following steps of:

s1, extracting shale surface three-dimensional elevation data and phase data through the processed AFM data, and correcting the shale surface three-dimensional elevation data;

s2, selecting a height threshold value by adopting a threshold value method, segmenting a pore function, calculating pore volume, and calculating the porosity of the shale according to the definition of the porosity;

s3, obtaining a phase pore function by adopting a dual-threshold discrete integration method, calculating the porosity in different phase intervals by utilizing the phase pore function, performing linear fitting on the porosity and the shale material composition in the different phase intervals, and calculating a correlation coefficient between the porosity and the shale material composition so as to evaluate the pore contributions of different components.

As an improvement, in step S1, performing elevation correction on the three-dimensional coordinate data of the shale surface topography with the elevation of the lowest point of the shale surface as a zero reference elevation.

In a modification, in step S2, the specific step of determining the pore volume is:

selecting a proper height threshold value, segmenting a pore function, regarding the projection of the surface of the sample on an xOy coordinate system as a virtual plane with negligible thickness, and cutting the surface of the sample from bottom to top by using the virtual plane, wherein the volume enclosed by the virtual plane and the surface of the sample lower than the plane is the pore volume, and the calculation formula is as follows:

wherein g (x, y) is a pore function; f (x, y) is an elevation function; t is a height threshold, m; v is the pore volume, m³(ii) a A is the projected area, m²(ii) a h is elevation, m; a and b are the projected width and length, m, respectively.

As an improvement, the step of calculating the porosity of the shale in step S2 is:

the volume is divided by the product of the projected area and the selected elevation, and is calculated as:

wherein phi is porosity,%.

As an improvement, the two-threshold discrete integration method in step S3 specifically includes:

on the basis of calculating the porosity by performing a threshold method on the elevation data once, performing a threshold method on the phase data once again, selecting a phase threshold value P, and segmenting a phase pore function, wherein the calculation formula is as follows:

where ξ (x, y) is the phase pore function; p is the phase threshold, °.

As an improvement, in step S3, the porosity in different phase intervals is calculated by using a phase porosity function, specifically:

integrating the difference between the elevation and the phase aperture function, and dividing the result by the product of the plane projection area and the elevation threshold value, wherein the formula is as follows:

wherein phi is_ξIs the phase porosity,%.

Compared with the prior art, the invention has the beneficial effects that:

1. the method for calculating the porosity of the shale and evaluating the contribution of the component pores based on the AFM widens the application range of the AFM in the field of unconventional oil and gas.

2. The method provides an idea for researching the pore contribution of different substance components of the shale gas reservoir, and lays a theoretical foundation for the fine characterization of the shale gas reservoir.

Drawings

FIG. 1 is a flow chart of an embodiment of the present invention;

FIG. 2 is a schematic view of a virtual plane cutting the surface of a sample from bottom to top; the three figures from top to bottom are sequentially schematic of the relative positions of the cut bottom surface, the middle position and the top surface;

FIG. 3 is a graph showing the correlation between the porosity and the main material composition in different phase intervals according to the present invention; in the figure, (a) is the correlation of the chlorite content and the phase interval porosity between-20 and-5 ℃; (b) the correlation between the content of the potassium feldspar and the porosity of a phase interval of-10 degrees is shown; (c) the correlation between the quartz content and the porosity of a phase interval of-5-15 degrees is obtained; (d) the correlation between the content of brittle minerals and the porosity of 0-10 degrees in a phase interval is obtained; (e) is the correlation of organic content with total porosity;

FIG. 4 is a graph of the temperature N achieved by the present invention₂Comparison of porosity measured by adsorption experiments.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below. It should be understood, however, that the description herein of specific embodiments is only intended to illustrate the invention and not to limit the scope of the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the terms used herein in the specification of the present invention are for the purpose of describing particular embodiments only and are not intended to limit the present invention.

Referring to fig. 1, the method for calculating the porosity of the shale and evaluating the contribution of the porosity of the shale based on the AFM comprises the following steps:

1) in the AFM scanning process, experimental errors such as sample substrate deflection caused by manual operation and scanning surface bowl-shaped deformation and noise interference caused by AFM probe swinging can occur, so that an AFM file needs to be guided into NanoScope Analysis software, noise reduction and proper-level flatten processing are carried out on a scanning image, and the experimental errors contained in the AFM file are reduced to the greatest extent;

2) exporting the three-dimensional elevation data and the phase data of the shale surface by utilizing Gwyddion software;

3) the derived elevation data are placed in a three-dimensional coordinate system, the image center is used as a coordinate origin, and the elevation of the lowest point of the shale surface is used as a zero reference elevation to correct the three-dimensional elevation data of the shale surface;

4) determining a pore function by judging whether the surface elevation function meets the requirement of an elevation threshold value by using a threshold value method so as to select pores in the AFM image, wherein the threshold value segmentation method can be expressed as the following formula:

wherein g (x, y) is a pore function; f (x, y) is an elevation function; t is a height threshold, m;

5) the projection of the sample surface on an xOy coordinate system is regarded as a virtual plane with negligible thickness, the sample surface is cut from bottom to top by the virtual plane, the volume enclosed by the virtual plane and the sample surface lower than the plane is the pore volume, and the calculation formula of the pore volume is as follows:

wherein V is the pore volume, m³(ii) a A is the projected area, m²(ii) a h is elevation, m; a and b are the projection width and length, m, respectively;

6) according to the definition of the porosity, the porosity is obtained by dividing the pore volume by the product of the projected area and the selected elevation, and the calculation formula of the porosity is as follows:

wherein, phi is porosity,%;

7) the phase pore function is obtained by using a dual-threshold discrete integration method, namely, changing the phase threshold on the basis of a fixed elevation threshold, wherein the dual-threshold discrete integration method can be expressed by the following formula:

where ξ (x, y) is the phase pore function; p is the phase threshold, °;

8) and calculating the porosity under the control of the phase threshold, wherein the calculation formula is as follows:

wherein phi is_ξPhase porosity,%;

9) and performing linear fitting on the porosity and the material composition in different phase intervals, calculating a correlation coefficient between the porosity and the material composition, obtaining the correlation between different components and the porosity in different phase intervals, and clarifying the corresponding relation between the phase intervals and the material composition so as to evaluate the pore contribution of the different components.

Wherein, the flat ten in the step 1) is generally selected to be 2 grades for shale samples.

Wherein, the correction method in the step 3) comprises the following steps: and subtracting the minimum value of the elevation values from all the elevation values to obtain a new elevation value.